The present invention relates to a process for producing L-glutamic acid by fermentation and more specifically, to a process for producing L-glutamic acid, by culturing an L-glutamic acid producing microorganism belonging to the genus Corynebacterium or Brevibacterium which organism has been mutated to acquire a temperature-sensitivity remediable with an unsaturated higher fatty acid.
A heretofore known microorganism capable of producing L-glutamic acid generally requires biotin to show adequate growth, while for the purpose of accumulating L-glutamic acid in a medium, the amount of biotin to be contained in a medium must be limited, or a substance which inhibits the action of biotin, such as is described in Japanese Published Examined Patent Application Nos. 1695/'65 and 8798/'65, must be added where a biotin-rich medium is used.
Those methods utilizing of such microorganism suffer from a number disadvantages. For example, in case of the method of limiting the amount of biotin in the fermentation medium the utilization of carbon sources, particularly inexpensive molasses is inevitably restricted; and that in case of the method of adding a substance which inhibits the action of biotin, the point addition and the amount of the substance constitute important factors and it is difficult to control the cultivation process.
The following operations wherein the production of L-glutamic acid is independent of the amount of biotin in the nutrient medium are also known.
One such process for producing L-glutamic acid by fermentation employs a microorganism belonging to the genus Corynebacterium which needs, for its growth or multiplication, not biotin but rather an unsaturated higher fatty acid such as oleic acid (Japanese Published Examined Patent Application No. 19632/75). The application also refers to a strain belonging to the genus Brevibacterium having similar properties to the Corynebacterium strain. This process, however, suffers from the economic and procedural disadvantage in that it is necessary to add to the medium an unsaturated higher fatty acid such as oleic acid whose cost is relatively high and to control the point of addition and the amount of the said compound. Alternatively, a process is known for producing L-glutamic acid by fermentation of a mutant belonging to the genus Brevibacterium whose growth is more likely to be influenced by temperature than the parent strain, as disclosed in Japanese Published Unexamined Patent Application No. 66687/77. It is reported that said microorganism has no requirement for oleic acid in Agricultural Biological Chemistry, 42 (10), 1911 (1978). Further, the yield is poor in terms of the productivity of L-glutamic acid to glucose. Thus, a need exists for a more reliable and economic method for the production of L-glutamic acid by fermentation techniques.